On Thu, 5 Jun 2008 09:33:58 +0200 Tom Cooksey <[EMAIL PROTECTED]> babbled:
> On Wednesday 04 June 2008 21:56:56 Andy Green wrote: > > | IMO, OpenMoko's choice of using the the glamo was a big mistake > > (Connecting it to a > > | shared, 4-bit bus was probably the _biggest_ mistake). > > > > Huh what? It's a 16-bit memory bus, maybe you mean 2^4 ;-) When I > > actually use the thing I don't notice much sluggishness. Your best bet > > is to eyeball one, I think you'll find it isn't the issue you think it is. > > I thought it was connected to the (4-wire) SDIO bus? it's on the memory bus, not sdio. a gfx chip on sdio would indeed be just about the most stupid idea i have ever heard of and anyone doing that should be summarily executed with a blunt spoon! :) > If it's connected to the address/data bus, why is it so slow and why can't > DMA be used to copy data to it? dma can. it just is even slower than using the cpu. also the entire memory bus is locked up when doing a copy with cpu OR dma, so even if dma were the same speed as doing a copy with the cpu, we'd still have the cpu locked out of the memory bus while waiting for dma - so no gain anyway (as in all practice you will need the memory bus :)). actual tests found dma to be LESS than 1/2 the speed of doing a copy with the cpu. this is just a limitation of the SOC, and the glamo is just well... not fast at accepting read/write requests - the bandwidth is limited to about 7mb/sec for writes ( can't remember what reads are - but i think its symmetric). so a big performance bottleneck we have is transfers to/from glamo - it really hobbles performance as it is a tiny straw we send data through. not to mention sd-card IO data also shares this glamo bus... :) so don't go doing any heavy IO on the SD card AND gfx... at the same time! :) -- Carsten Haitzler (The Rasterman) <[EMAIL PROTECTED]> _______________________________________________ Openmoko community mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/community
